Sakura Zensen

Japan takes its cherry tree blossom, sakura (桜), very seriously. For centuries, Japanese have flocked to view the cherry blossoms and held traditional hanami picnics under the blooming trees.


Tracking the cherry blossom season is a science all unto itself. The Japan Meteorological Agency forecasts the “cherry blossom front” (sakura zensen), as it makes its way through the country. The front starts in January in the southern islands of Okinawa and ends in early May in the northern island of Hokkaido. The agency also developed a formula to compute this forecast. Here it is:

DTS = \exp ((9.5\times10^3).(\frac{T - 288.2}{288.2T}))

(If you want to compute the forecast yourself, it’s a piece of cake. DTS represents the number of days converted to standard temperature, and T stands for the temperature in Kelvin).

The official day of the start of the season is determined when 80% of the flowers on sample trees, tracked by the agency, have blossomed. There are apparently exactly 59 sample trees across the country.

Japanese follow this forecast closely and plan their hanami accordingly. Some make special travel plans to prime viewing locations. Companies organize picnics and send junior staff to rope off areas in popular parks well in advance. This year, due to the particularly warm winter, sakura zensen is attracting particular attention. In fact, I was in Okinawa last month (December) and saw a couple of flowers blossoming. Unfortunately, I didn’t know whether the trees I saw were part of the sample or not…


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